Such a switching gas damper, as has been disclosed by EP 0 437 151 B1, has the object of assisting the effect of an arc quenching device for low-voltage power circuit breakers which switch in air. The arc quenching device causes switching arcs which occur during operation of the power circuit breaker to be quenched without adversely affecting the power circuit breaker itself, adjacent system parts, or other assemblies. These arc quenching devices or arcing chambers have very different physical forms, depending on the type, the physical size and the switching rating demanded of the power circuit breaker. These devices all have the common feature of a more or less parallel arrangement of arcing plates composed of sheet steel and arranged transversely with respect to the switching arc.
In order to reliably quench switching arcs, the switching gases produced do not have to be cooled down to room temperature. At least when the rating of an arc quenching chamber is fully utilized, it is thus possible for gases to emerge from the arcing chamber at a temperature that is considerably greater than room temperature. Metal vapor residues can thus also be carried with the gases, and there may be a certain amount of ionization. The installation type of power circuit breaker governs whether such phenomena are harmless. Fundamentally, it can be stated that an amount of metal vapor and residual ionization become less acceptable the shorter the distance between the outlet openings from the arc quenching chambers and adjacent live or grounded components. This distance is an important cost factor in the construction of switchgear assemblies, since the dimensions of the switchgear assemblies depend on it.
On the other hand, the cost rises when arc quenching chambers are designed such that they satisfy the most stringent requirements with regard to the characteristics of the switching gases that occur. For this reason, the approach has therefore been adopted of equipping low-voltage power circuit breakers with standard arcing chambers which result in a given switching rating, but which represent a compromise between the minimum and maximum requirements with regard to the characteristics of the switching gases that occur. For situations in which a power circuit breaker must be accommodated in a particularly space-saving manner in a switchgear assembly, additional switching gas dampers are provided, according to the cited EP 0 437 151 B1, and are common to all the arcing chambers.
The known switching gas damper forms a shroud, which covers all the arcing chambers in the power circuit breaker. Before the switching gases can escape from the shroud, they flow through a cooling grid and an outlet filter. The upward flow direction of the switching gases is not influenced by this. This may be undesirable, if there is only a small amount of space above the power circuit breaker. Furthermore, the process of collecting the switching gases from all the arcing chambers in a common space requires an adequate volume in order to avoid an electrical phase flashover in all circumstances.